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javascript/snippets/unzip-with.md

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+---
+title: Ungroup array elements based on function
+type: snippet
+tags: [array]
+cover: coconuts
+dateModified: 2022-01-23T13:18:50+03:00
+---
+
+Creates an array of elements, ungrouping the elements in an array produced by [zip](/js/s/zip) and applying the provided function.
+
+- Use `Math.max()` and the spread operator (`...`) to get the longest subarray in the array, `Array.prototype.map()` to make each element an array.
+- Use `Array.prototype.reduce()` and `Array.prototype.forEach()` to map grouped values to individual arrays.
+- Use `Array.prototype.map()` and the spread operator (`...`) to apply `fn` to each individual group of elements.
+
+```js
+const unzipWith = (arr, fn) =>
+  arr
+    .reduce(
+      (acc, val) => (val.forEach((v, i) => acc[i].push(v)), acc),
+      Array.from({
+        length: Math.max(...arr.map(x => x.length))
+      }).map(x => [])
+    )
+    .map(val => fn(...val));
+```
+
+```js
+unzipWith(
+  [
+    [1, 10, 100],
+    [2, 20, 200],
+  ],
+  (...args) => args.reduce((acc, v) => acc + v, 0)
+);
+// [3, 30, 300]
+```